Lipids

Fatty acids:

• can be branched or unbranched.

• are highly oxidized storage forms of hydrocarbons.

• are referred to as “saturated” if they have one or more C–C double bonds

• never exceed 20 carbons in length, by definition

Answer explanation

Fatty acids are carboxylic acids with hydrocarbon chains ranging from 4 to 36 carbons long (C4 to C36). In some fatty acids, this chain is unbranched and fully saturated (contains no double bonds); in others, the chain contains one or more double bonds. A few contain three-carbon rings, hydroxyl groups, or methyl-group branches.

What is the advantage of storing energy in the form of triacylglycerol over glycogen? 

• Triacylglycerol has a lower melting temperature

• Glycogen hydrolysis is poorly regulated

• Because triacylglycerol is bigger, it takes up more space inside the cell

• Because triacylglycerol is hydrophobic and excludes water, it takes up less space

Answer explanation

One significant advantage to using triacylglycerols as stored fuels rather than glycogen is triacylglycerols are hydrophobic and therefore unhydrated. Because of this, the organism that carries stored fuel in the form of fat does not have to carry the extra weight of water of hydration that is associated with stored polysaccharides (2 g per gram of polysaccharide).

Which sphingolipids have a single monosaccharide as a component?

• cerebrosides

• gangliosides

• globosides

• plasmalogens

Membrane lipids do NOT include:

• glycerophospholipids

• triacylglycerols

• sphingolipids

• glycolipids

Answer explanation

Triacylglycerols are primarily used for storing energy and providing insulation in animals. They are not structural lipids in membranes.

Mass spectrometry:

• cannot be used with lipids other than fatty acids.

• can determine the mass but not the identify of a lipid

• can be used to identify individual lipids in complex mixtures

• cannot determine the locations of double bonds in a fatty acid

Answer explanation

With the increased resolution of mass spectrometry, it is possible to identify individual lipids in very complex mixtures without first fractionating the lipids in a crude extract — the “shotgun” approach.